We view Equation REF  from the perspective of causal intervention. A typical causal graph including \(m\)  as a mediator variable is shown in Figure REF . The approach of causal intervention relies on the do-calculus [1]}. Specifically, when applying the \(\text{do}(\cdot )\)  operation on the input variable \(X\) , we are trying to intervened \(X\)  to the observed value \(x\)  denoted by \(\text{do}(X=x)\) . After the do-calculus, \(x\)  (represented by \(R\)  in practice) is not determined by other variables. In other words, all the arrows pointing to \(x\)  will be cut off while the arrows from \(x\)  to other variables remain. It means that, for the mediation causal graph, causal intervention will let \(p(y| \text{do}(R)) = p(y| R)\)  which does not modify Equation REF .
